Whole point is to not change tooltip height, album art can be larger that entire screen or smaller than 16x16, so the solution is to scale image to current aspect ratio. Otherwise it can lead to inconsistency.

Staring at these screenshots again, it occurs to me that the artist and title are unnecessarily repeated in the current UI: once right under the app name, and again towards the bottom, on the transparent bar. We can probably get rid of one of these to scrounge up some more vertical space for the album art.

Staring at these screenshots again, it occurs to me that the artist and title are unnecessarily repeated in the current UI: once right under the app name, and again towards the bottom, on the transparent bar. We can probably get rid of one of these to scrounge up some more vertical space for the album art.

Noticed the same thing but didn't think it was part of the patch. It would be nice if the information wasn't repeated. +1

How about this? I'd send a new patch if it's possible to change 2 things in one patch.

I was thinking here that you might have to visually prioritize the content and controls.

For example, instead of having the playback buttons on a small corner on the bottom right, have them centered and a little bigger. I would remove the duplicate song title. In the end, the user will probably want to interact with the popup more than trying to read the labels. In my mind, the user appreciates the content but his primary action is to work with the controls. Therefore, those controls should have more visual prominence.

Looking real good. Big props for keeping the same tooltip height as in all other situations. For reference here's what it looks like with a light scheme:

The only thing I'd do now is add a just a little bit of a left margin for the artist & track info, and the same as a right margin for the player controls. But that could be done in another patch anyway.

The only thing I'd do now is add a just a little bit of a left margin for the artist & track info, and the same as a right margin for the player controls. But that could be done in another patch anyway.

Yep, just do this and I think the patch can land. It's fine to do that here IMO.

...Either that, or don't extend the blurred background so low that it's underneath the text and controls, in which case the existing built-in margins become acceptable.

How about adding a little bit of a margin above the song name (Layout.topMargin 2, same as the left margin)
And why not keep the level of the track name at 4? It's more important than the artist name (subheading)

Before:

After:

The difference in heading levels matches up really nicely with our notifications, for example:

The song name is more important (more 'current' and calls for more attention, especially when skipping through an album).

I don't think the topMargin is needed because there is already a space between the song name and the cover image. My goal is to keep the cover image as big as possible.

It looks stuck on. And considering that this patch shrinks the album art a great deal already (and we seem to deem that to be an acceptable side effect), sacrificing the margins to get more album art size doesn't make sense.

I propose that you also add a right margin (2 px) to offset the one on the left.

P.S. We could also implement this in latte-dock. Not just that, but also give latte's ToolTipInstance a makeover (the fonts are really huge).
I've actually already used this diff to modify latte-dock's ToolTipInstance:

Might be worth another patch? I could post my changes or if you want you could write your own version :D

P.S. We could also implement this in latte-dock. Not just that, but also give latte's ToolTipInstance a makeover (the fonts are really huge).

No problem... Concerning Latte, just a side note, we discussed this with @trmdi when he initially submitted the first version of this patch for Latte.
My decision for this is that whatever the official plasma taskmanager supports as a design decision the same will be applied to Latte also. I want
the Latte Preview windows to look the same with plasma taskmanagers one. So this patch I think is an effort from @trmdi to update the plasma
taskmanager previews in order afterwards to apply the same thing to Latte....

Again no problem from me, as long as the Latte and plasma taskmanagers have same Preview Windows

Might be worth another patch? I could post my changes or if you want you could write your own version :D

no problem, I would propose first to have an acceptance from here and afterwards create a new PR for Latte

HInt: Please dont discuss here the Latte case because it creates noise for all the reviewers interested in this